Developers have been promoting their products through in-game billboards since at least mid-1980s, but ArsTechnica writes about an entirely new twist:

"In Dungeon Siege 2: Broken World, our forum goer Scero found an NPC [non-playing character] that told him about the Dungeon Siege PSP game and offered him a code for it, as well as saying the PSP game had a code for items in the game he was playing."